1. Field of the Invention
The present invention relates to a method for weft insertion in a jet loom and an apparatus for carrying out the same and, more particularly, to a method for weft insertion in which a weft measuring roller is rotated in synchronism with the crankshaft of the loom to draw out a weft from a supply package, and an apparatus for carrying out the same.
2. Discussion of the Related Art
A jet loom measures and stores a weft of a length substantially corresponding to the width of a cloth being woven or to a length of two-thirds the width of the cloth prior to weft insertion, and then inserts the stored weft into the warp shed together with a jet of fluid for weaving by a main nozzle.
Japanese Utility Model Publication No. 50-13976 (1975) discloses a weft measuring device of a winding type. This known weft measuring device comprises a driving roller, a weft measuring roller pressed against the driving roller, and a grooved guide held on a fixed shaft disposed in parallel to the shaft of the weft measuring roller. In this known weft measuring device, the weft is wound several times around the weft measuring roller and the grooved guide, and the weft measuring roller is rotated to draw out the weft from a supply package by a predetermined length.
Japanese Patent Publication No. 38-21811 (1963) discloses a weft measuring device comprising a weft measuring roller and a pressure roller disposed opposite to the weft measuring roller. This known weft measuring device draws out a weft from a supply source weft by the measuring roller and the pressure roller pressed against the weft measuring roller and measures the length of the weft through the detection of rotation of the weft measuring roller. Another known weft measuring device is of a wind arm type.
Also known are weft storage devices of different types for storing a weft of a measured length, namely, a weft storage device of an air pool type which accumulates and stores a weft of a measured length in a floating condition by air, a weft storage device of an adhesion type which accumulates and stores a weft of a measured length in a zigzag shape on a moquette like, adhesive accumulating surface, and a weft storage device of a drum type which accumulates and stores a weft of a measured length in coils on a drum.
A weft measuring, accumulating and inserting operation of a jet loom employing the known weft measuring device of a winding type and a weft storage device of an air pool type will be described hereinafter with reference to FIG. 8.
A weft Y drawn out from a cheese 1, a supply package of the weft, through a tension control device 2 is coiled at a fixed speed for measuring around a weft measuring roller 5 rotating in synchronism with the rotation of the crankshaft of the loom and a guide 6 having a plurality of circumferential grooves 6a while the weft Y coiled around the weft measuring roller 5 and the guide 6 is blown into an accumulating pipe 9 of the weft storage device by an air current produced by a blowing 7 device of the weft storage device, and the weft Y blown into the accumulating pipe 9 is extended in a V-shape and is kept in a floating condition within the accumulating pipe 9 by an air current produced within the accumulating pipe 9 in the direction of an arrow A.
The weft Y accumulated and stored in the accumulating pipe 9 is drawn out through a longitudinal slit 9a formed in the wall of the accumulating pipe 9, and is guided through an eyelet 10 formed in the blowing device 7, a gripper 11 for alternately gripping and releasing the weft Y in a appropriate timing and a yarn guide 10a to a main nozzle 12.
In inserting the weft Y into the warp shed, the gripper 11 releases the weft Y immediately after the main nozzle 12 jets air, to draw out the weft Y from the accumulating pipe 9 through the slit 9a and to insert the weft Y into the warp shed. Then, the weft Y is carried by the jet of air along a guide channel S defined by air guide plates 13 for insertion. Upon the insertion of the weft Y by a length corresponding to that of a pick, the gripper 11 grips the weft Y to complete a weft inserting operation by stopping the further insertion of the weft Y into the warp shed.
The weft Y being drawn out from the cheese 1 at a constant drawing speed by the weft measuring roller 5 rotating at a constant speed is accumulated in the accumulating pipe 9 in a floating condition with the leading end thereof gripped by the gripper 11 for the next weft inserting cycle.
The length of the weft Y to be accumulated in the accumulating pipe 9 is dependent on the operating speed of the loom and the length of picks. Ordinarily, the length of the accumulated weft Y is on the order of two-thirds a length necessary for one picking cycle. Accordingly, the weft Y is supplied to the accumulating pipe 9 at a comparatively low speed, and then the accumulated and stored weft Y is drawn out from the accumulating pipe 9 at a high speed for weft insertion. The length of the accumulated weft Y extending in a V-shape along the accumulating pipe 9 between the wall 7a of the blowing device 7 and the eyelet 10 decreases gradually as the weft Y is inserted into the warp shed and, near the end of the weft inserting cycle, the accumulated weft Y extends in a line from an output of the blowing device 7 in the wall 7a to the eyelet 10. Generally, a running mode of the weft Y in a period from the start of weft insertion to a moment when the weft Y extends in a line between the exit of the blowing device 7 in the wall 7a and the eyelet 10 is designated as a free running mode. The running speed of the weft Y at the main nozzle 12 in the free running mode is represented by Vp. Thereafter, the weft Y measured by the weft measuring roller 5 is supplied directly to the main nozzle 12 without being accumulated in the accumulating pipe 9 in a floating condition and is inserted into the warp shed by the jet of air jetted by the main nozzle 12. Generally, a mode of running of the weft Y under this weft condition without accumulation is designated as a constrained running mode. In the constrained running mode, the weft Y runs at a running speed Vf coinciding with the surface speed of the weft measuring roller 5, i.e., a weft drawing speed drawn from the weft source, because there is no accumulated floating section in the weft Y. The weft measuring roller of the conventional measuring device is interlocked with the crankshaft of the loom, and hence the weft measuring roller rotates for measuring operation, except during a transient period subsequent to the start of the loom and a transient period precedent to the termination of the operation, at a constant surface speed Vf defined by: Vf=Lo/tc, where Lo is the weft length and tc is a time necessary for one weaving cycle of the loom.
FIG. 9A is a graph showing the variation of the running speed V of the inserted weft Y as measured at the main nozzle 2 with time, and FIG. 9B is a graph showing the variation of the tension T of the inserted weft Y as measured at a position between the guide 10a and the main nozzle 12 with time. When the running mode of the weft Y changes from the free running mode to the constrained running mode, the running speed V at the main nozzle drops suddenly from Vp to Vf as shown in FIG. 9A, and a peak tension Tp appears in the tension variation curve as shown in FIG. 9B at the moment when the running speed drops from Vp to Vf. At the end of the constrained running mode, namely, when the gripper 11 grips the weft Y upon the completion of inserting the weft Y by a predetermined length, the running speed of the weft Y drops suddenly from Vf to zero and the tension T resulting from the sudden variation of the running speed V increases sharply to another peak tension To. The relation between the variation of the running speed V and that of the tension T with reference to FIGS. 9A and 9B shows that the variation of the tension T is substantially proportional to the variation of the running speed V.
An increase in the operating speed of the loom entails an increase in the running speed difference Vp-Vf, hence an increase in the peak tension Tp. In some cases, the peak tension Tp exceeds the tensile strength of the weft Y so as to damage or break the weft Y or to spoil the running condition of the weft Y causing faulty weft insertion.
The weft storage device of an air pool type needs disadvantageously an accumulating pipe having an increased length, hence a large space for installation, when applied to a loom having an increased reed width.
Weft storage of an adhesion type device suffers from the drawbacks of an increase in weft tension when the running mode of the inserted weft changes from a free running mode to a constrained running mode and the need for a large space for installation when applied to a loom having a large reed width.
The weft storage device of a drum type suffers from weft breakage liable to occur when the running mode of the inserted weft changes from the free running mode on to the constrained running mode, increase in the number of coils of the weft on the weft metering drum when applied to a loom having a large weft length, and the resultant increase in the frequency of entanglement of the coils and faulty weft insertion.